For various reasons which are well known in the art, it is useful or necessary from time to time to spot acid or some other chemical in a particular place downhole in a well (such as an oil well). For example, hydrochloric acid, which will dissolve more than 10 cubic feet of rock per thousand gallons of 15% acid concentration, the usual strength employed, is used to work on natural or induced fractures in limestone or dolomite. The acid is usually put into the tubing and is followed by water to force the acid down the tubing to the formation being treated. This water and the acid that has been "spent" on the formation rocks must be carefully placed. Similarly, it may be desirable to employ certain chemicals in a "soak" mode in order to remove corrosion, scale, or the like from the casing walls. Again, accuracy of placement is an absolute necessity for obtaining meaningful results. Those skilled in the art will appreciate that such spotting operations are normally carried out by utilizing techniques in which circulation to the surface is obtained. That is, a pump forces fluid down the tubing and back up through the casing to the surface to be over-boarded or recirculated. The known volumes of the tubing and casing permit accurate spotting to be obtained by simple calculation of the displacement of fluid pumped into the casing after the chemical charge has been introduced therein.
However, in some old or established wells, it is impossible or prohibitively difficult to obtain such circulation because of a loss of bottom hole pressure resulting from the age of the well or the type of formation being produced. Additionally, in some new wells, it is undesirable to spot a fluid in hole because of the extra amount of load water required to do so. By using the subject tool, trip time can be significantly cut down on work-overs.
Thus, those skilled in the art will appreciate that it would be highly desirable to achieve accurate chemical spotting in a well within which circulation-to-the-surface techniques cannot economically be employed in the usual manner.
It is therefore a broad object of my invention to provide improved means for spot treating an oil well or the like downhole with liquid chemicals.
It is another object of my invention to provide such means which may be employed without the necessity for achieving fluid circulation to the surface.
Still another object of my invention is to provide such means which is simply and reliable in operation and which is economical to fabricate.